Industry forecasts predict that future generation Hard Disk Drives will use two-stage actuator architectures in order to achieve higher track densities. Piezo milli-actuators are being proposed as a possible second actuator to be combined with conventional voice coil motors (VCM) for the two-stage implementation.

We have developed models for the milli-actuator and evaluated performance of TI electroncis when controlling such actuators. The milli-actuator is mathematically modeled as a second order system. Transfer functions for displacement vs. input voltage and velocity vs. input voltage have been measured; the measurements also show that the piezo milli-actuators exhibit hysteresis under voltage driving. TI' Samuel chip provides two driving modes for piezo milli-actuator: voltage driving and charge driving. The charge-driving mode is modeled in Matlab Simulink, and operation of the IC is verified by comparing time and frequency simulations to measurement. Charge mode driving is compared to voltage driving in terms of transfer function under both room- and high-temperatures. The total transfer function from DAC to displacement is measured under different driving amplitude for charge mode. DSP code has also been implemented and is ready for demonstrating close loop control of milli-actuators.